1. Field of the Invention
The invention relates to a blast system for processing components by means of abrasive particles, comprising a hopper for abrasive particles, a mixing device formed by a mixing chamber into which an HP-air pipe issues and which in its turn issues into a blast pipe, a transport line between the hopper and the mixing chamber through which the abrasive particles are transported from the hopper to the mixing chamber, means for generating HP-air which is supplied to the mixing chamber through the HP-air pipe for obtaining a mixture of air and abrasive particles which issues from the blast pipe, and a transport mechanism for transporting the abrasive particles through the transport line.
2. Description of the Related Art
Abrasive blast systems are mainly used for cleaning surfaces (blast cleaning), removing burrs from surfaces (deburring), and introducing compression stresses into a surface for raising the fatigue limit (shot peening). A fairly new application is the shaping of components of brittle material, for example for making a plurality of small cavities and/or holes in a plate of electrically insulating material as described in EP-A-0562670 (PHN 14.374). Accuracy is of major importance here. A high accuracy can only be obtained when it is ensured that both the flow density of the abrasive particles and the air output with which an operation is carried out are constant as much as possible. Thus it was found that the accuracy of the holes in the plate is strongly dependent on the inflow of the abrasive particles into the mixing chamber. The transport of the abrasive particles from the hopper to the mixing chambers is obtained in most blast systems through the creation of an underpressure in the mixing chamber by means of HP-air connected to the mixing chamber. The abrasive particles are attracted by suction owing to the underpressure. A major portion of the power supplied by a compressor is necessary for generating this underpressure. It is found, however, that the underpressure created in the mixing chamber by means of the HP-air does not lead to an even flow of abrasive particles from the blast pipe during the process. The system must therefore be provided with a separate transport mechanism for the abrasive particles. U.S. Pat. No. 3,139,705 discloses a sandblasting system, in particular for sandblasting of ships, wherein the transport of the abrasive particles is achieved by means of a vibratory mechanism, and not by means of an underpressure generated with HP-air. All these blast systems have operated until now at absolute HP-air pressures of approximately 7 bar. It requires very much power, however, to obtain such high pressures. Their use in mass manufacture is therefore very inefficient. Lowering of the operational pressure, however, is no solution because the speed with which the mixture leaves the blast pipe becomes too low, which is also inefficient.